The present invention relates to a method for braking a traction sheave elevator and to a traction sheave elevator.
The present invention relates to a method for braking a traction sheave elevator and to a traction sheave elevator.
The machinery a traction sheave elevator includes a traction sheave with grooves in which the elevator hoisting ropes are fitted and an electric motor driving the traction sheave either directly or via a gear. The machinery comprises a brake which acts on the traction sheave either directly or e.g. via a shaft. The working principle of the operating brake of an elevator is such that the brake is forced to brake always when it has not been specifically commanded not to brake. In a typical operating brake construction, the brake is closed by the force of a spring or an equivalent element and opened and kept open by a controlled actuator counteracting the force of the closing element. When the traction sheave is braked, the braking effect is transmitted to the hoisting ropes by the agency of frictional grip and other gripping effects applied to the ropes by the traction sheave. In an emergency braking situation, when the elevator is stopped as quickly as possible, the braking system is likely to be required to provide a greater gripping force than during acceleration and deceleration in a normal operating situation.
To increase the grip between the ropes and the traction sheave, especially in fast elevators and elevators with a large hoisting height, the traction sheave is sometimes provided with grooves having a very large undercut angle. The frictional grip can also be improved by increasing the angle of contact of the rope. The solutions used to increase the contact angle include e.g. ESW (extended single wrap) and double-wrap suspension, in which a contact angle exceeding 180xc2x0 between the traction sheave and the ropes is achieved by using a crosswise rope arrangement or a secondary rope pulley. In conventional single-wrap (CSW) suspension, the contact angle between the traction sheave and the ropes is 180xc2x0 or somewhat less if the distance between the ropes has been increased by using a diverting pulley. In short, the friction can be increased by using undercut rope grooves and increasing the undercut angle and by increasing the angle of contact.
In a normal operating situation in most elevators, including fast elevators and those with a large hoisting height, a conventional suspension with the hoisting ropes only running over the traction sheave and a moderate undercut angle of the traction sheave grooves would be sufficient to guarantee a non-slip grip of the ropes on the traction sheave in all load situations of the elevator. However, to allow for emergency braking, the system must be designed to provide a better grip. However, improving the grip leads to drawbacks that increase elevator costs, especially costs arising during operation. Undercut rope grooves promote wear of the rope and rope groove, and the larger the undercut angle, the faster the wear. Similarly, rope bends following each other in close succession in ESW and double-wrap suspension increase rope wear. In ESW and double-wrap suspension, an oblique rope contact is an additional factor increasing rope wear. Double-wrap suspension imposes an extra load on the bearings of the traction sheave and the secondary rope pulley.
The object of the present invention is to extend the use of the basically simple conventional elevator suspension system to faster elevators and elevators with a larger hoisting height and to improve the operating characteristics of elevators like those used at present. The invention is also applicable for the correction of the above-mentioned drawbacks.
The solution of the invention makes it possible to achieve a longer useful life of the ropes and traction sheave. The drive machinery can be implemented using a solution in which the internal stresses are small, which means e.g. a lower load on the bearings. The useful life of the ropes, traction sheave and bearings may even be increased to multiple times the original service length. In general, simpler solutions can be applied in the machinery and rope system. Since CSW suspension does not require any diverting pulley arrangements in the machine room, the floor area required by even a very large elevator is reasonable. No heavy support structures for diverting pulley arrangements are needed. The moderate size and weight of the machinery achieved by the invention allow a simpler machine room lay-out and easier installation. High-performance machines are often used in elevator groups comprising several elevators, in which case the possibility of easy placement provides a pronounced advantage i respect of space utilisation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.